December 25 , 2016:

by Elsa Panciroli

I was looking at Romer’s Gap the other day. No this isn’t a dirty confession, although I did come back with sand in my hiking boots. Just before Christmas I found myself digging into the fine shingle of a beach opposite Bass Rock, near Edinburgh, in the pouring rain. Beside me were three burly men with shovels, who were undoubtedly making faster progress than I. We were digging down 350 million years into Scotland’s past, in search of bones from a time when the fossil record falls eerily silent: this is Romer’s Gap.

There are often periods of geological time where conditions were not good for fossil preservation, or the creatures that lived didn’t preserve well (such as the very earliest boneless, squishy lifeforms over 540 million years ago). In some cases we haven’t found the right rocks of that age yet, or we can’t access the rocks, for example if someone has peskily built a city on top of them. Occasionally these fossil gaps represent true low points in diversity – there simply weren’t very many animals in existence to then die and become fossilised – but often the fossils have just not been uncovered yet.

Romer’s Gap is a global missing page, a time when the record of tetrapods, our four-limbed vertebrate ancestors, is scanty at best. It was first recognised by the famous and prolific palaeontologist, Alfred Romer, and so it was given his name. The lack of information is a real snag, as it is also when our earliest terrestrial ancestors evolved the key features that would let them breathe air, lift their bodies out of the water, and, 350 million years later, wrap their cold digits around the handle of a shovel on a rocky beach in Scotland.

It turns out Scotland holds some key pieces. The men sweating away on the beach shovelling sand had invited me to join them in digging up fresh evidence. The first was Dr Stig Walsh, Senior Curator of Vertebrate Palaeobiology at the National Museum of Scotland (NMS), Edinburgh. Alongside other scientists from the Museum, the Universities of Cambridge, Leicester and Southampton, and the British Geological Survey, Stig is part of the TW:eed project, working to find out more about the earliest tetrapods from Romer’s Gap, as well as fleshing out whole ecosystems during this 20 million year fossil blackout.

“The tetrapods we know from the latest Devonian would have been strange to our eyes,” Stig explains to me as we pause for a quick break from digging. “They had far too many digits for one thing, and probably wouldn’t have been able to come far onto land. After the Gap the tetrapod fauna is diverse and well adapted for walking on land, but we just had no information on how this had happened or why.” Putting on his gloves, he picks up his shovel and continues - “fortunately for us, Scotland has an amazing fossil record; the answers were here all along.”

After scratching our way over a metre downwards through the shingle, we finally hit the waterworn rocks of the early Carboniferous. The four of us took a break to drink coffee and chat about the site. Dr Tom Challands, teaching fellow at the University of Edinburgh and TW:eed Associate Partner - known as “The Lungfish Doctor” by his colleagues – was hoping to find the fossils of his moniker. It looked promising: “that’s definitely a lungfish tooth,” he cries, unabashedly dropping to his knees to examine a bright fleck in the rock beneath him, “I reckon we might get lucky and find some bone.”

Previous research has suggested that vertebrates became smaller during Romer’s Gap. Changes in body size have important repercussions for our understanding of ecosystems over the long-term, so any change in fish and other vertebrates at this time would have important ecological consequences. “The only thing is,” points out Tom, “that previously there was only one definitive species of lungfish known from this time period – that’s only one data point. We can’t really tell what happened to them without more data.”

The final person in our team was Matt Dale, owner of Mr Wood’s Fossil Shop in Edinburgh. He had visited this beach some years previously alongside the late and well-respected Scottish fossil hunter, Stan Wood. This was one of many sites around Edinburgh Stan frequented, finding internationally important plant and animal fossils, such as Westlothiana lizziae: a lizard-like creature that bears the name of the area in which it was found. Matt reminisced about Stan’s talent and persistence in looking for fossils; a determination necessary for all palaeontologists, whether amateur or professional.

Our samples were packed in protective foam and loaded into backpacks for the hike back to the car. On the way Stig told me about the upcoming exhibition at the National Museum of Scotland, Fossil Hunters: showcasing some of the important Scottish contributions to early tetrapod palaeontology, and celebrating the people, like Stan Wood, who uncovered them. Through our work that day on the beach, we could count ourselves amongst those people.

A few weeks later I caught up with Tom in his office, regarding the rucksacks of rock we had trudged back to the car that rainy afternoon in North Berwick. His eyes widened with delight as he showed me seven new species of lungfish identified from the site we’d been digging. “Turns out lungfish were actually getting bigger during Romer’s gap,” he explained, the exact opposite of previous studies. “They just didn’t have enough information before – this is why the work TW:eed is doing is so important, we have to find more evidence if we want to understand what was happening to life back then.”

Fossil Hunters: Unearthing the Mystery of Life on Land opens at the National Museum of Scotland on the 19th February until the 14th August. Admission is free. #FossilHunters
The TW:eed Project
Sallan, L. and Galimberti, A.K., 2015. Body-size reduction in vertebrates following the end-Devonian mass extinction. Science, 350(6262), pp.812-815